Absorbable polyglycolic acid suture of enhanced in-vivo strength retention

ABSTRACT

Polyglycolic acid in shaped form (i.e., a suture) which is substantially free from vaporizable impurities is provided which has significantly greater in-vivo strength retention than shaped polyglycolic acid containing said vaporizable impurities. The improved polyglycolic acid is prepared by vacuum heating shaped polyglycolic acid containing vaporizable impurities to vaporize the impurities therefrom, and then removing the vaporized impurities from the polyglycolic acid. An apparatus for conveniently carrying out the above process is also provided.

United States Patent I 1 3,626,948

[72] Inventors ArthurGlick 5 k f r cig d Ph C UNITED STATES PATENTS c 3,297,033 1 1967 Schmittetal 128/3355 3331814 7 1967 Randall 12s/335.5x 21 A LN. 786049 Decn 1968 3,371,069 2/1968 Miyamaeetal. 12s/33s.5x '3,422,l8l 1 1969 Chirgwin 264/345 [45] Patented Dec. 14, 1971 [73] Assignee American Cyanamid Company Primary Examiner-Dalton L. Truluck Stamford, Conn. Attorney-James T. Dunn ABSORBABLE POLYGLYCOLIC ACID SUTURE OF ABSTRACT: Polyglycolic acid in shaped form (Le, a suture) ENHANCED lN-VIVO STRENGTH RETENTION which is substantially free from vaporizable impurities is provided which has significantly greaterin-vivo strength retention 2 Claims, 8 Drawing Figs.

than shaped polyglycolic acid containing said vaporizable im- Cell Ala/3 3253 purmm The improved polyglycolic acid is prepared by I Fie'ld 128/334 vacuum heating shaped polyglycolic acid containing vaporizable impurities to vaporize the impurities therefrom, and then 335's; 161/172; 264/345 removing the vaporized impurities from the polyglycolic acid. An apparatus for conveniently carrying out the above process is also provided.

SIZE /0 SUTURE (AVERAGE VALUES S/ZE 2-0 SUTURE Ml 'fiAGE VALUES) //V-V/ V0 TENS/LE STRENGTH (PSI //V THOUSANDS) TENS/LE STRENGTH (PSI IN THOUSANDS) g1 TENS/LE STRENGTH (PSI IN THOUSANDS) PATENIED ntcman 3,525,94

SHEET 1 F 7 /00 EFFEcr 0F TEMPERATURE (PRESSURE: 4 mm. Hg TIME 5 HOURS) I 90 PACKAGE STRAIGHT PULL /.5 Q 70 q PACKAGE mar PULL Q, 1 Q 50 /.0 3

k WEIGHT Loss 3 r" i 30 a I /5 DAY/N-V/l/O gym/aw TEMPERATURE ("a l /0 r- EFFECT OF PPEssUPE TEMPE/PA rUPE 55 a TIME 5 HOURS) 9 A .9 Q E 8 J .8 g ISDAY w-v/ v0 STRAIGHT PULL E 7 k 6 .6 k /c /vm0L 1 k 5 P x v .5 4 3 FR WE/GHT L055 5 4 0 i l 1 L l ABSOLUTE PRESSURE (mm/1g) NWNTURS ARTHUR SLICK [31A ME S 8. Ma PHERSON, JR.

AGENT PATENTED Bit 1 4 l97l SHEET 2 [IF 7 EFFECT OF HEAT/N6 TIME {PRE$$URE-' 4mm. Hg)

Exam :65 8 3 p55: a.

HEAT/N6 TIME IHRS.)

IN VENTORS. ARTHUR GL/CK gAMES B. M0 PHERSON, JR.

{Wm M 22,41

AGE/VT lN-V/VO TENS/LE STRENGTH (PSI IN THOUSANDS) PATENTEUnzmmn 3152 34 SHEET 3 OF 7 Q SIZE /0 .SUTURE (AVERAGE VALUES) SIZE 2-0 .SUTURE {AVERAGE VALUES) DAYS lMPLA/VTED m/ RABBI/T fIE. 4

mvlsw'mkg, ARTHUR GL/CK Fig/MES 5. M6 PHERSON, JR.

/N-V/V0 TENS/LE STRENGTH {PSI l/V THOUSANDS) PATENTED ntumm 31525349 SHEET [1F 7 DATA EXTRAPOLAT/O/V TREATED SIZE 2-0 SUTURE CONTROL SIZE 2-0 .S'U T URE /5 DAYS IMPLA/VTED //V RABBIT fIE7. 5

INVIINTORS,

A THUR 6L ICK JAMES B. McPHE/iSO/V BY AGE/VT PATENTEB 05mm 332594 sum 5 {1F 7 mvrsmoze.

ARTHUR 6/. /CK JAMES B. McPl-IERSOMJR.

PATENTED DEC! 4 I9?! SHEET 8 BF 7 INVENTORS. ARTHUR GL/C'K JAMES B. McPHERSO/V, JR.

BY fm-ulm (4f AGENT PATENTEDmunn 3152594 l i -40 38 l I I [32 I P, 33 I {a 430 23 5H 39 27 I 35 V mam? I 37 l/VLH" l6 1 w: I g /5 24 /5 VACUUM SYSTEM |-M VAR/ABLE Ramp Pia/08747 INVENTORS,

ARTHUR G'L/CK JAMES B. MCPHERSO/V, JR.

BY Rama. a1. 1%

ABSORBABLE POLYGLYCOLIC ACID SUTURE OF ENHANCED IN-VIVO STRENGTH RETENTION BACKGROUND OF THE INVENTION For many years, virtually all absorbable sutures used in animal and human surgery were prepared from mammalian intestine, such sutures being commonly called catgut sutures.

More recently, widespread research efforts have been directed toward discovery of a synthetic material which could be readily extruded into filaments from which sutures could be fabricated which would (l) retain their tensile strength after implantation in the body for a sufficient time to permit wounds joined together with such sutures to heal properly and (2) would be absorbed by the body without adverse effects and within an acceptable time after implantation. Such a material would have many advantages over catgut such as uniformity of composition and, hopefully, ease of manufacture. These efforts have recently borne fruit. U.S. Pat. No. 3,297,033, for example, described a synthetic absorbable suture prepared from polyglycolic acid, said patent herein incorporated by reference.

Polyglycolic acid can be prepared in a variety of ways. For example, it can be prepared by heating glycolic acid and then removing water and glycolide from the resulting material after which a catalyst is added to the residue and the residue heated (U.S. Pat. No. 2,585,427). It can also be prepared as described above except that the residue is cooled and collected as a powder which is then heated at an elevated temperature (U.S. Pat. No. 2,676,945). It can additionally be prepared by the polymerization of glycolide which is free from water and acid impurities in the presence ofa catalyst (U.S. Pat. No. 2,668,162).

In order to obtain the strong filaments of polyglycolic acid which are suitable for use as absorbable sutures, it is necessary that the polyglycolic acid used to prepare the filaments have a relatively high-molecular weight (i.e., in the range of 10,000 or more). It is now established that if polyglycolic acid of sufficiently high-molecular weight for use as a suture is desired, the preferred route to such a polymer is by the polymerization of glycolide as described above. During the polymerization, some glycolide monomer fails to polymerize to polyglycolic acid and glycolide contents in the polymer of as much as about 8 percent have been observed.

Although entirely acceptable sutures can be prepared from polyglycolic acid containing glycolide, applicants have discovered that:

I. when glycolide and other impurities which either react with the glycolide or are formed as byproducts of a reaction of glycolide with a reactive impurity are removed from the polyglycolic acid to the extent possible by vaporization of the impurities, and

2. these vaporized impurities are then removed from the environment of the suture, that sutures prepared from such substantially" impurity-free polymer exhibit an astonishing enhancement in in-vivo strength retention as compared to sutures prepared from polymer which contains these impurities. ln-vivo strength retention is determined by implanting suture lengths in rabbits and then sacrificing the rabbits at prescribed intervals (usually 7 and/or 15 days after the implantation), whereupon the suture is removed and the tensile strength of the suture measured in accordance with standardized procedures.

With the advent of an absorbable polyglycolic acid suture, some attempts havebeen made to raise the in-vivo strength retention to previously unattainable values while at the same time assuring absorption of the suture by living tissue within a reasonable time. Ordinarily, it is desirable that an absorbable suture retain a surgically useful tensile strength for up to 10 to days after implantation; it is equally important that the suture be absorbed by tissue soon thereafter, preferably within 90 days after implantation. it would, of course, be most desirable if a suture could be provided which gave consistently high in-vivo tensile strength even after 15 days implantation in tissue while simultaneously being substantially absorbed by the tissue within about days after implantation. Achievement of these dual requirements in catgut absorbable sutures can present problems because treatments which enhance in-vivo strength retention of the suture may extend the absorption period appreciably. For example, when catgut sutures are chromicized to enhance in-vivo strength retention, conditions must be very carefully controlled to prevent excess chromicizing; otherwise, suture absorption times can be unduly prolonged.

U.S. application Ser. No. 551,947, filed May 23, 1966 now U.S. Pat. No. 3,422,181, issued Jan. 14, 1969 teaches that invivo strength retention can be improved in a polyglycolic acid suture by merely heating the suture at certain temperatures and atmospheric pressure for a given period of time. However, the improved strength of the suture results primarily from an annealing effect within the polyglycolic acid filaments since, under the conditions described in the application, an effective amount of impurities would not be removed from the polymer if they were present therein. Also the application does not teach the importance of removing any volatilized impurities from the environment of the suture as will be discussed hereinbelow in greater detail. This is not surprising since, as mentioned above, little, if any, effective volatilization of impurities occurs under the process conditions of this application.

is is an object of this invention, therefore, to provide a new kind of shaped polglycolic acid which is substantially free from vaporizable impurities and which, as a result thereof, exhibits consistently high in-vivo tensile strength even after 15 days implantation in living tissue.

It is another object to provide shaped polyglycolic acid having consistently high in-vivo strength retention after 15 days while, at the same time, being substantially absorbed by living tissue within 90 days after implantation.

It is also an object of this invention to provide a novel process and apparatus which are eminently suitable for preparing the polyglycolic acid of this invention.

SUMMARY OF THE INVENTION This invention relates to polyglycolic acid in shaped form which is substantially free from vaporizable impurities.

The term polyglycolic acid or polyglycolic acid in shaped form" as used herein refers to any of the continuous forms into which polyglycolic acid can be fabricated such as by extrusion, molding or such and includes monofilaments, multifilaments, sheets, film, rod, ribbons, and molded objects; it also includes polyfilamentary braided strands useful as absorbable sutures and variously shaped body implants and prosthetic devices such as described in copending application Ser. No. 608,068, filed Jan. 9, 1967 now U.S. Pat. No. 3,463,151, issued Aug. 24, 1969. The invention will be described in terms of a polyglycolic acid multifilamentary braid suitable for use as an absorbable suture for purposes of clarity; however, the invention is also applicable to various other shaped forms of polyglycolic acid as described above.

A "vaporizable impurity is one which can be volatilized from the polyglycolic acid.

Polyglycolic acid is substantially free from vaporizable impurities" when it exhibits a weight loss of less then 0.4 percent by weight when it is heated for 3 hours at C. under an absolute pressure of 4 mm. of mercury in the presence of a cooled surface maintained at a temperature of about 25 C., said surface being separated from the polymer by a distance of about 2 inches. As the polyglycolic acid is heated, the vaporizable impurities contained therein are vaporized and diffuse across the gap between the polymer and the cooled surface. As the impurities strike the cooled surface they condense to produce a residue on the surface whereby the impurities are removed from the environment of the polyglycolic acid.

As described heretofore, the removal of these impurities has a pronounced effect upon the in-vivo strength retention of a shaped form of polyglycolic acid such as a suture. The impurities removed are believed to consist primarily of water, glycolide, and the linear dimer of glycolic acid which is represented by the formula:

These impurities can arise in the polyglycolic acid in a variety of ways. For example, as described heretofore, glycolide can originate from unpolymerized monomer. If a polyglycolic acid suture containing glycolide is exposed to a moist environment the suture may pickup water. It is believed that this water reacts readily with the gylcolide to cleave the glycolide ring and form the aforementioned linear dimer of glycolic acid. It is further believed that the linear dimer of glycolic acid can then react with the high-molecular weight polyglycolic acid in a transesterification reaction to produce sutures having polyglycolic acid chains of lower molecular weight which tend, when implanted in living tissue, to give reduced retention of in-vivo tensile strength.

The impurities may also arise if the polymer is subjected to high temperatures which tend to partially degrade it. For example, polyglycolic acid is extruded at a temperature of about 240-250 C. and it is possible under these conditions that some polymer can degrade into glycolide or the linear dimer of glycolic acid. Ofcourse, the glycolide thus formed can react with any moisture present to form additional undesirable linear dimer. Because of the reactive interrelation between water and glycolide to produce the undesirable linear dimer, it is essential that all three of these impurities i.e., water, glycolide, and the linear dimer of glycolic acid be removed. The degree to which the in-vivo strength retention is enhanced is believed to depend upon the extent to which the vaporizable impurities present are removed from the polymer. Ordinarily, as a greater proportion of these impurities is removed, a greater enhancement of in-vivo strength retention is noted.

This invention also relates to a process for preparing polyglycolic acid in shaped form which is substantially free from vaporizable impurities which comprises heating shaped polyglycolic acid containing vaporizable impurities in a dry environment at a temperature of from about 75- C. to about 160 C. at a subatmospheric pressure. Under these conditions an effective amount of vaporizable impurities contained in the polyglycolic acid is removed therefrom. Once these impurities are removed, it is essential to further remove them from the immediate environment of the heated polyglycolic acid. If this is not done, the impurities have a strong tendency, especially when pressures which are not subatmospheric are restored, to condense upon the surface of the polymer to produce a white powdery surface coating on the polymer. These impurities also tend to polymerize to harmful higher molecular weight forms and cannot be removed from the polymer thereby causing an irretrievable loss of the polymer.

In cases where this deposition of impurities on the surface of the polyglycolic acid has occurred, the in-vivo as well as package properties of the polymer were most unsatisfactory indicating the highly undesirable effect these impurities can produce. Therefore, means must be provided, once these impurities have been vaporized, for removing them from proximity with the polyglycolic acid. A particularly suitable way for effecting this removal is to provide a cooled surface adjacent to the heated polymer, the cooled surface being maintained at a temperature below that of the heated polymer. After the vaporized impurities are removed from the polymer, they diffuse towards the cooling surface and condense thereon whereby they are removed from the environment of the polymer.

This invention also relates to an apparatus for removing and collecting vaporizable impurities from polyglycolic acid in shaped form. In its most basic aspects, the shaped polyglycolic acid member is supported in an airtight chamber. Means are provided for applying heat to the member within the chamber.

Means are also provided for the creation of subatmospheric pressures within the chamber. The housing containing the chamber is adapted to provide for cooling at least a portion of the wall of said chamber adjacent to the heated member, this portion of the chamber wall being separated from the heated member by a predetermined distance. As the member is heated within the chamber under subatmospheric pressure, vaporizable impurities contained therein are vaporized and diffuse across the gap separating the heated member from the cooled portion of the chamber wall. As the impurities strike the cooled portion of the chamber wall they condense thereon to effect removal of the impurities from the environment of the polyglycolic acid member.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 depicts the effect of the temperature at which a polyfllamentary braid is heated upon various properties of the braid and upon the weight loss exhibited by the braid.

FIG. 2 depicts the effect of the pressure at which a polyfilamentary braid is heated upon the in-vivo strength retention of the braid and the weight loss exhibited by the braid.

FIG. 3 depicts the effect of heating time upon the in-vivo strength retention of a polyfilamentary braid and the weight loss exhibited by the braid.

FIG. 4 depicts the enhanced in'vivo strength retention achieved by the process of this invention as shown by a comparison of the in-vivo properties of polyfilamentary braids treated in accord with the process of this invention and braids not so treated.

FIG. 5 depicts the significant upgrading in in-vivo strength retention which can be achieved by the process of this invention by comparing the in-vivo properties of polyfllamentary braids which ordinarily have little, if any, in-vivo tensile strength after 15 days implantation in living tissue with the invivo properties observed on the same braids after treatment in accordance with the process of this invention.

FIGS. 60 and 6b represent an exploded view of an apparatus which is suitable for preparing the shaped polyglycolic acid of this invention.

FIG. 7 is a center, sectional view of the assembled apparatus of FIG. 6 further including various equipment for controlling process conditions within the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Polyglycolic acid as typically prepared in U.S. Pat. Nos. 2,668,I62, or 3,297,033, is conventionally extruded into a multifllament which is then divided into various portions for use as sleeves and cores during braiding. A braided polyglycolic acid suture is prepared from these portions using conventional braiding techniques and equipment. A portion of the braid thus prepared is weighed and then wound circumferentially around a hollow metal cylinder. The cylinder-braid unit is weighed and placed within an Erlenmeyer flask with the axis of the cylinder perpendicular to the bottom surface of the flask. The flask is immersed in an oil bath maintained at a temperature about 5 C. higher than that at which it is desired to heat the braid. The upper portion of the flask is not immersed in the oil and is exposed to a room temperature environment. The appropriate subatmospheric pressure is then established in the flask. The impurities contained in the braid vaporize and diffuse to the inner surfaces of the flask which are not below the oil line, these surfaces having a temperature substantially below that of the heated braid. The impurities col- Iect on these surfaces as a noticeable white powdery residue. After heating for the prescribed amount of time, the cylinderbraid unit is removed from the flask and weighed; this weight is subtracted from the original weight of the cylinder-braid unit to determine the quantity of impurities removed from the braid. The percent weight loss of the braid is determined by dividing the quantity of impurities removed by the original weight of the braid and multiplying by I00. The package properties, i.e., straight pull and knot pull, are measured on both unsterilized braid and braid sterilized by gaseous ethylene oxpackage and in-vivo properties. The in-vivo and weight loss ide. There is ordinarily no detectable difference in package data of table 11 are presented graphically in FIG. 2. These data properties between sterilized an unsterilized braid. Sterilized indicate that the pressure at which the suture is heated has virbraid is then implanted in rabbits for a period of 7 or days, tually no effect upon the package straight pull and knot pull; after which the braid is removed from the animal and its ten- 5 however, pressure does have a pronounced effect upon the insile strength measured, said value being the in-vivo tensile vivo tensile strength of polyglycolic acid. Referring to FIG. 2, strength. The straight pull is readily measured using a Scott it can be seen that it is essential that the suture be heated Inclined Plane Tester (Model N mber 1P4) i accord i h under conditions of subatmospheric pressure. Merely heating h th d shown i U. s, P XV, P 938. K ll i at atmospheric pressure, although it does remove some similarly measured in accord with the procedure shown in U. 10 Volatiles. has no appreciable effect "P ill-vivo smmglh- This S, P, XV, Pg, 939, is not surprising since it would be expected that glycolide or Th method described imm di t l h i b was d the linear dimer of glycolic acid would be removed in any apto gather the data in table; I to V h einbei preciable amount at such pressures. However, as pressure is gradually reduced below I atmosphere there is a greater in- PROCESS CONDITIONS crease in the amount of impurities removed from the suture with a corresponding increase in the in-vivo tensile strength of a. Temperature: the suture. It is not until pressures below about 300 mm. of

Th Cffec! o mp r tur 6011818"! Pr and h g mercury are reached that the weight loss and corresponding im p n p g n ini pr perti and upon he enhancement of in-vivo tensile strength becomes readily apweight loss of sutures treated in accordance with the process parent although some weight loss and enhancement of tensile of this invention is shown by the data of table I. These data are strength does occur at pressures in excess of 300 mm. of mergraphically presented in FIG. 1. Referring to FIG. 1, it is obcury but less than 1 atmosphere. it is, of course, desirable that served that no appreciable weight loss occurs until the filathe pressure be maintained at as low a value as possible; presment is heated to at least a temperature of 75 C. As soon as sures below about 100 mm. of mercury are preferred and presappreciable amounts of impurities begintos tpoglz frop th suresof from 0.1 to 4 mm. of mercury are highly preferred.

TABLE II.-EFFECT OF PRESSURE (5 HRS. AT 135 C.)

Package properties 15-day in-vivo properties Straight pull Knot pull Straight pull Percent Percent Percent weight Diameter incre se increase Pressure (mm. Hg) loss (mils) Pounds P.s.l. Pounds P.s.l. Pounds P.s.l. in lbs. in P.s.l.

filament, there is a noticable enhancement in the 15 day inc Heating Time: vivo straight pull value of the suture. This improvement continues until temperatures in excess of about I60 C. are em- Th ffe t of heating time (at constant pressure a d P y whereupon there is a Sharp decrease in ill-vivo strength stant temperature) is shown by the data of table 111. The data as well as package straight pull and knot pull. It sho be of table iii are shown graphically in FIG. 3. Referring to FIG. not h gh I 0f lhe Suture increases a! a r y 3, it can be seen that the amount of volatiles removed from a Slam Yale as temperature incleases 3 temperature of suture at a fixed heating time depends somewhat on the temabout 160 to 180C. is reached where pon shap an perature at which the suture is heated with more volatiles matic increase in the amo nt of vol iles eleas by h being removed as higher temperatures are used. However, reture occurs suggesting that at these elevated temperatures gardless of temperature, the largest portion of vaporizable imrapid thermal degradation of the polymer is beginning to ocpurities is removed during the first hour of heating with only cur. Preferred heating temperatures are from about 100 to 0 minimal additional removal occuringas heating continues. 150 C. The data of table I indicate that in-vivo strength reten- The degree to which in-vivo strength of the suture is tion can be improved by as much as 222 percent when the suenhanced appears to roughly parallel the amount of volatiles ture is treated within the preferred temperature range given removed from the suture at least at temperatures within the above. 7 V Mmw HWWM V prescribed temperature range, (see the dotted 135 C. curve TABLE I.THE EFFECT OF TEMPERATURE (4 MM. Hg. FOR 5 HOURS) 16-day in-vivo properties Package properties Straight pull Percent Straight pull Knot pull Percent Percent wt. Diameter m Diameter increase increase Temperature C.) loss (mils) Pounds P.s.l. Pounds P.s.l. (mils) Pounds P.s.l. in lbs. in p.s.i.

Control 13. 4 10. 8 76, 600 7. 3 51, 800 13. 8 74 4, 900

b. Pressure: in FIG. 3). On the other hand, when excessively high tempera- Data are presented in table 11 which show the effect of prestures i.e., about [60 C., are used, although there is significant sure (at constant temperature and heating time) upon 5 removal of volatiles, there isamarked decrease in the in vivo 7 8 strength of the suture as clearly shown by the dotted 180 C. Table V presents data which indicate how poiyglycolic acid curve of FIG. 3. As discussed above, this is believed to occur sutures formerly having little, if any, tensile strength after l5 at temperatures above 160C. because the volatiles which are days implantation in living tissue were upgraded by treatment removed are no longer merely the undesirable impurities in accordance with the process of this invention to sutures not which are removed at temperatures below 160 C. but are the 5 only having acceptable 15 day tensile strengths but also having thermal degradation products of polyglycolic acid as well. The p g y g y Values- For p one case. a suture can be heated from about 5 minutes to about 24 hours, lure which P "calmem y the F of this ihvemh)" the heating time generally inversely proportional to had virtually no day tensile strength exhibited a tensile the temperature at which the suture is heated. Preferred heat- ,su'euglh of 7338 after treatment by the Process by ins limes range from about 1 to 5 hours l invention. Selected average data from table V are shown in a preferred embodiment, a polyglycolic acid filament, graphically m F multifilament, braided yarn, or such is heated at a temperature of about l00 to I50 C. for about 3 hours under an absolute pressure of 1 mm. of mercury or less.

invention can be dyed, coated, needled, sterilized, packaged, and used in accordance with techniques described for the i5 polyglycolic acid suture disclosed in US. Pat. No. 3,297,033.

TABLE IIL-EFFECT OF HEATING TIME (4 MM. Hg AND CONSTANT TEMPERATURE) -day in-vivo properties Package properties Straight pull Straight pull Knot pull Percent Percent Temp. Percent Diameter Diameter increase increase Time (hrs.) C.) wt. loss (mils) Pounds P.s.i. Pounds P.s.l. (mils) Pounds P.s.i. in lbs. in p.s.i.

15. 7 14. s 76, 500 9.7 50,100 15. 7 14. 6 75, 500 9. 2 7, 500 16. 1 15. 8 77, 600 9. 4 46, 200 15. 4 14. 5 77, 900 9. 2 49, 400 15. 7 14. 2 73, 400 9. 1 47, 000 16. 1 15.7 77, 100 9. 1 44, 700 "ifzi""iiIFifH "7f"54{766"""" 13. 2 9. 6 70, 200 6. 6 48, 200 13. 4 10. 3 73, 000 7. 3 51, 800 13. 2 9. 2 67, 300 6. 7 49, 000 13.2 10.4 76,000 7.4 54,000 16. 1 16. 2 79, 600 9. 4 46, 200 15. 0 13. 7 69, 000 8. 7 43, 800 15. 9 12. 1 61, 000 8. 9 44,800 16. 1 12 9 63,400 9. 0 44,200 15.9 11.1 55,000 7.8 39,300 Table IV presents data which has been gathered on a variety APPARATUS of difi'erent sized polyglycolic acid sutures which have been FIGS, 6 d 6b reprgseml d d views f a ferred treated in accordance with the process of this invention and 40 embodiment f an a ar t hi h i i l l i ble f serves to indicate the astonishing increases in in-vivo strength removing and collecting vaporizable impurities from a retention g as 282 P which Occur when y polyglycolic acid filament in accordance with the process of small amounts of volatiles are removed from the this invention. The exploded view of the apparatus is best seen Selected averaged data from table IV are shown graphically In by placing FIG. 65 on top of FIG. 6a to obtain an overall exg FIG. 4. V 45 ploded view of the apparatus.

TABLE IV.-EFFECT UPON PACKAGE AND IN-VIVO PROPERTIES OF POLYULYCOLIC ACID SUTURES Package properties Straight pull I n-vivo straight pull 1 Percent Percent Diameter change change Percent Suture size (mils) Pounds I.s.i. in lbs. Pounds P.s.l. in lbs. wt. loss Comments 1 8 20. 7 74, 700 4. 3 16, 500 Control. 18 9 20. 1 71, 600 3 4. 7 16, 400 +9 0. 67 Treated.

l-0 13.4 11.4 81, 000 1. 23 8, 700 Control. 13. 4 11. 3 80, 000 1 2. 69 19, +119 41 Treated l3. 4 11.7 83, 000 .91 450 Control 13.5 12. 1 84, 500 +2 3. 47 21, 900 +282 59 Treated 13.5 11.2 78, 300 2.1 14, 700 Control 13. 5 11. 0 76, 900 2 3. 3 22, 700 +57 62 Treated 13. 0 9. 0 67, 800 1. 2 8, 700 Control 13. 1 9. 1 68, 600 1 1. 5 10, 900 +25 .64 Treated 14. 0 13. 3 86, 400 2.1 13, 600 Control 13. 6 12.5 86, 100 6 3. 2 21, 100 +53 67 Treated 14, 3 10. 6 65, 900 20 1, 200 Control 14. 4 10. 3 64, 000 3 76 4, 700 +280 .67 Treated 13.6 12. 7 88, 800 1 5 10, 500 Control. 13.3 12. 7 91, 500 0 3 8 27, 400 +164 76 Treated.

20 10. 6 7. 15 82, 300 1 2 13, 900 Control. 10. 7 6.8 75, 200 5 1 3 14, 500 +8 45 Treated. 11. 7 7. 8 73, 600 38 3, 500 Control. 11. 9 ,7. 3 65, 900 6 78 7, 000 54 Treated. 10.3 6. 4 76, 400 65 6, 600 Control. 10.2 6. 5 79, 600 +2 1,03 12, 600 +87 84 Treated. 10. 4 6. 1 71,800 .44 5, 200 Control. 10. 1 5. 9 73, 700 3 09 12, 400 1. 04 Treated.

3-0 9. 9 4 83, 200 .69 8, 970 Control. 10. 1 6. 8 8 +6 1 70 21,200 +147 86 Treated.

1 After 15 day implantation in rabbits, Control: as is; treated: subjected to C. and 4 mm. Hg for about 5 hours.

The devolatilized sutures prepared in accordance with this TABLE V.UPGRADING OF POLYGLYCOLIC ACID SUTURE BY APPLICATION OF DEVOLATILIZATlON TREATMENT THERETO In-vivo straight u ll after implantation in la 5 for- Package properties 7 days 15 days Percent Percent Percent Suture Diameter change change w size (mils) Pounds P.s.l. in lbs. Pounds P.s.i. in lbs. Pounds P.s.l. loss Comments 1 18. 6 89 3, 275 0 Control. 18. 6 8. 8 32, 270 +880 74 2, 700 1. 3-2. Treated. 1-0 13. 2 31 9, 500 0 0 Control. 13. 2 5. 4 39, 200 +310 1. 08 Treated. 2-0 10. 8 80, 200 0 Control. 11.0 1.03 Treated. 10. 5 1. 61 18, 500 Control. 10. 5 4. 78 55, 000 +197 1. 52 Treated. 10. 6 64 100 Control. 10. 6 2. 67 30, 800 +395 026 Treated. 10. 2 2.81 34, 300 0 Control. 10. 2 2. 60 3], 800 7 39 4, 770 Treated. 10. 0 1. O 12, 700 Control. 10. 1 4. 02 51, 200 +302 945 12, 000 1. 32. 5 Treated.

Referring to FIGS. 6a and 6b, and to FIG. 7, a center sectional view of the assembled apparatus, this apparatus comprises metallic baseplate 11 supported by legs 12. Baseplate 11 contains groove 13 which is adapted receive gasket 14. Baseplate 11 contains threaded apertures 15 which are adapted for insertion of thermocouples up through plate 11 into the apparatus (see FIG. 7). Baseplate 11 also contains threaded aperture 16 adapted for connection to a vacuum system (see FIG. 7). Gasket 14 is placed within groove 13.

Support plate 17 is placed upon baseplate 11 and firmly attached thereto by screws 18 which are threaded into holes 19 in baseplate 11.

High-resistance wire 20 is wrapped around hollow metallic cylinder 21 to provide a heating element. Leads 22 of wire 20 pass through apertures 23 in the wall of cylinder 21 and into the interior of cylinder 21. Cylinder 21 containing wire 20 is then inserted through recess 23a of plate 17, the bottom surface 24 of cylinder 21 coming to rest on surface 25 of baseplate 11. Lead wires 22 emerge from the apparatus through aperture 25a in plate 11 connecting to variable rheostat 26 (see FIG. 7). Aperture 25a is adapted for airtight passage of leads 22 into and out of the apparatus such as by a Stupekof tube. Plate 17 is secured about base 27 of cylinder 21 by setscrews 28. Spacing collar 29 is then inserted over the top portion 30 of cylinder 21 by setscrews 31.

Polyglycolic acid suture braid 32 is circumferentially wrapped around hollow metallic cylinder 33. Cylinder 33 is adapted at top portion 34 and bottom portion 34a to receive screws 35 which facilitate subsequent removal of the cylinder (while still hot) from the apparatus by means of a wire handle. Cylinder 33 containing braid 32 is carefully slid over collar 29 and cylinder 21 coming to rest on surface 36 of support plate 17. Collar 37 of support plate 17 and collar 29 insure that the inner surface of column 33 is uniformly spaced in distance from the outer surface of wires 20 so as to provide uniform heating of braid 32.

Hollow cylinder 38 which is adapted 39 for passage of a liquid-cooling medium through annular space 40 (see FIG. 7) between inner wall 41 and outer wall 42 is then slid over cylinder 33 and braid 32 contained thereon coming to rest on gasket 14 which is mounted in groove 13 of plate 11. Gasket 43 is placed on the top surface 44 of cylinder 38, and lid 44a is placed on top of gasket 43 to complete assembly of the ap paratus.

Referring to FIGS. 6a, 6b, and 7, it will be noted that the apparatus contains provisions for the insertions of three thermocouples by means of apertures 15. One thermocouple 45 measures temperature on the outside surface 46 of circumferentially wrapped braid 32. A second thermocouple 47 measures temperature of the inner surface 48 of cylinder 33. A third thermocouple 49 measures the temperature of wire 20.

These three thermocouples are connected to temperature recorder 50 for easy monitoring.

The temperature of wire 20 can be adjusted to produce the desired temperature at inside wall 48 and the surface 46 of braid 32. The temperature of wire 20 required to produce any given temperature at surface 46 of braid 32 will of course vary depending on the thickness of airgap 51 between cylinders 27 and 33 as well as on the thickness of wall 52 of cylinder-'33. Generally, where the width of gap 51 is about 1 inch and where the thickness of wall 52 is about one-eighth of an inch, the temperature of wire 20 can vary from about 210 to 290 C., corresponding to an inner wall 48 temperature of from about to 205 C. and to a temperature at the outer surface 53 of wall 52 of from about I00 to about C.

After the apparatus is assembled the appropriate vacuum is applied through aperture 16 and power is applied to wire 20, said power being adjusted by rheostat 26 to create the aforementioned desired temperature at the various points in the apparatus. After a brief induction period, the temperature of braid 32 is raised to a sufficiently high value to cause the vaporization of any vaporizable impurities contained therein. Cooling water having. been previously applied to annular space 40 of cylinder 38, the vaporized impurities from braid 32 diffuse across gap 54 which separates heated braid 32 from cooled inner surface 55 of cylinder 38 contacting cooled surface 55 and condensing thereon whereby their removal from the environment surrounding braid 32 is effected.

The thickness of. gap 54 can vary considerably provided there is a finite distance between outer surface 46 of braid 32 and surface 55 of cylinder 38. Ordinarily, a gap distance of up to about 12 inches is suitable with a distance of about I to 2 inches high preferred.

If the radial thickness of braid 32 becomes excessive, the temperature of braid 32 in contact with surface may have to be in excess of 160' C. in order to insure a suitably high temperature at the surface 46 of braid 32 which is closest to cooled surface 55, thereby creating a risk of damaging braid closest to hot surface 53 of wall 52. However, when thicknesses of less than one-half inch are used in the described apparatus, suitable temperatures can be produced throughout the entire radial thickness of braid 32. The acceptable radial braid thickness will, of course, depend on the particular design of the apparatus.

Table VI presents data gathered using the apparatus described in FIGS. 6a, 6b, and 7. In all cases, there was improvement in the in-vivo strength retention of the sutures treated on the apparatus as compared to untreated sutures. It should be noted that although samples were taken from various radial thicknesses of braid 32, in-vivo strength improvement was noted in all cases. The data of table VI also indicate that there is substantially no difference in package straight re ies? kneire lbetweer.Lewd e a i a ed r 'lAllLE VI. -POLY(1LYCOLIC ACID SUIURES F ENHANCED IN-VIVO STRENGTH RETENTION PREPARED Wllll 'lllE APPARATUS OF mas. m, 6b AND 7 'lmnpomturo 0.) ol Package properties day ln-vivo properties Outer wall Inner wall I Straight pull Knotpull Straight pull Outside of braid of braid Heating Location of Diameter Braid length braid cylinder cylinder element sample 1 (mils) Pound p.s.i. Pound p.s.i. Pounds p.s.i

Control 10. 3 5. 5 66, 000 3. 6 43, 200 0 0 100 113 147 213 1 9. 7 5. 4 73, 100 3. 7 50, 100 29 4, 000 100 113 147 213 2 9. 9 5. 2 67, 600 3. 8 49, 400 3, 300 100 113 147 213 3 9. 8 5. 0 66, 300 3.6 47, 700 11 1, 500 127 160 200 280 1 10. 3 5. 4 64, 800 3. 8 600 13 1. 600 127 160 200 280 2 10. 4 5. 3 62, 400 4. 1 48, 200 14 1, 600 127 160 200 280 3 10. 5 4. 9 56, 600 3. 7 42, 300 12 1, 400 101 114 148 215 1 10. 1 6. 4 79, 900 4. 4 900 014 170 101 114 148 215 2 10. 4 6. 1 71, 800 3. 7 43, 600 71 8,400 101 114 148 215 3 10. 3 6. 6 79, 200 4. 6 55, 200 71 8, 500 128 162 202 283 1 10. 2 5. 3 64, 900 4. 0 49, 000 01 120 128 162 202 283 2 9. 5 4. 4 62, 100 3. 4 800 03 420 128 162 202 283 3 l0. 1 5. 6 69. 900 4. 3 53, 700 25 3, 100

1 Sample Location 1: braid in contact with the outer wall of the braid oi the braid, i.e. the braid furthest removed from the outer wall of the cylinder; Sample Location 2: braid midway between Location 1 and the braid cylinder. outside wind of the braid; Sample Location 3: braid from the outside wind We claim: being further characterized by a weight loss of less than 0.4 1. An absorbable surgical prosthesis which is compatible in percent by weight when said polyglycolic acid is heated for 3 living tissue comprising a filamentary strand structure of 25 hours at 135 C. underapressure of 4 mm. of mercury. synthetic tissue absorbable material for use as a suture or liga- 2. The prosthesis of claim 1 wherein the polyglycolic acid is ture, said absorbable material consisting of polyglycolic acid, a surgical suture. substantially free of vaporizable impurities, having substan- =1- e a s s tially enhanced in-vivo strength retention characteristics and 

2. The prosthesis of claim 1 wherein the polyglycolic acid is a surgical suture. 